1. Field of the Invention
The present invention relates to a fluxgate sensor for measuring an azimuth angle and a method thereof, and more particularly, to a fluxgate sensor which is capable of obtaining calibrated azimuth even at slope by using a neural network, and an azimuth measurement method thereof.
2. Description of the Related Art
A fluxgate sensor operates to measure intensity and orientation of terrestrial magnetism, which are unperceivable by human sensory systems. More specifically, a fluxgate sensor uses a fluxgate to detect terrestrial magnetism. The fluxgate sensors can find the accurate orientation of a place of detection based on the detected terrestrial magnetism, and are widely used in many applications such as navigation devices in automobiles, and map services for mobile phones and portable terminals.
The fluxgate sensor detects the size and orientation of an external magnetic field by applying an excitation magnetic field to a high permeability magnetic material such as permalloy through a driving coil, and measuring a secondary frequency harmonic, which is in proportional relation with the external magnetic field, by using the magnetic saturation of the magnetic core and nonlinear magnetic characteristics.
Fluxgate sensors were first introduced in late 1930. Fluxgate sensors provide more advantages than other types of terrestrial magnetic sensors, such as higher sensitivity, cheaper price and compactness. Furthermore, the fluxgate sensors consume less power than other sensors, and also have long-term stability. As a result, fluxgate sensors have been applied in a variety of areas for both commercial and military use, which include detection of weak magnetic field, absolute terrestrial directions, exploration for vein of ore, target search, positioning of an artificial satellite, and space exploration. Fluxgate sensors are continuously researched for better performance.
Recently, as the micro electro mechanical system (MEMS) technology is introduced, many efforts have been made to develop a micro-sized fluxgate sensor with low power consumption. If developed, this new type of fluxgate sensors will further enhance performance of the terminal devices such as portable telephones. However, considering that the portable devices are carried around by users, the compactness of the fluxgate sensor must be guaranteed and this compromises the stable detection. The portable device faces almost every direction as the user holds it in hand and moves around, and further, the portable device changes directions almost constantly. This means that the fluxgate sensor implemented in the portable device is subject to countless direction changes to any slope angle, and accordingly, a method is required to protect the fluxgate sensor from the influence of sloping by real-time basis, and automatically compensate for the signal detected therefrom.
FIG. 1 is a block diagram of a conventional fluxgate sensor. Referring to FIG. 1, the fluxgate sensor 100 has a driving pulse generating circuit 101, a coil driving current amplifying circuit 102, a two-axis fluxgate 103, a chopping circuit 104, a primary amplifying circuit 105, a low-frequency filter 106, a secondary amplifying circuit 107, an A/D converter 108, a controller 110, a slope detection device 120, and a memory 130.
The driving pulse generating circuit 101 generates a driving pulse to drive the two-axis fluxgate 103, and selectively switches the driving pulse to apply to the coil driving current amplifying circuit 102. The coil driving current amplifying circuit 102 uses a number of amplifiers and inverters to output a pulse signal and an inverted pulse signal at opposite phase with each other from the pulse outputted from the driving pulse generating circuit 101.
The two-axis fluxgate 103 includes X-axis and Y-axis fluxgates. Accordingly, the two-axis fluxgate 103 is driven by the pulse signal and inverted pulse signal transmitted to the X-axis and Y-axis fluxgates, and outputs a detection signal corresponding to the electromotive force which is generated by the driving thereof. In FIG. 1, two rectangular-ring magnetic cores are placed with their lengths aligned to X and Y axes, respectively, and the driving coil and detection coil are wound around the magnetic cores, respectively. Upon application of the driving pulse through the driving coil, a magnetic field is generated from the X-axis and Y-axis fluxgates, and therefore, the induced electromotive force can be detected through the detection coil.
The electric signal, which is detected from the two-axis fluxgate 103, is chopped at the chopping circuit 104 through proper control on the number of internal switches of the chopping circuit 104. After the chopping, the electric signal is amplified at the primary amplifying circuit 105 by differential amplification, and then a certain range of signals are filtered through the low-frequency filter 106, and finally amplified in the secondary amplifying circuit 107. After the amplification, the signals are converted to digital voltage values through the A/D converter 108 and the outputted.
To represent 3-dimensional space by using X, Y, Z axes, the slope detection device 120 is configured as a two-axis acceleration velocity sensor having an X-axis acceleration velocity sensor placed in x-axis and a Y-axis acceleration velocity sensor placed in y-axis. The slope detection device 120 operates to calculate the pitch and roll angles of the slanted position by using the signals obtained when slanted toward the gravity of the earth. In other words, the slope detection device 120 measures pitch and roll angles by inspecting the movement of a certain weight according to gravity, through the use of visual tools or electric circuits such as a goniometer, a scale or an indicator needle. The measured pitch and roll angles are stored in the memory 130.
When the induced electromotive force, detected at the two-axis fluxgate 103, is processed through a series of processes to be inputted as digital values, the pitch and roll angles stored in the memory, the dip angle in the current position, and the digital value inputs are substituted in a series of equations to calculate an azimuth.
However, according to the conventional way as described above, because pitch and roll angles are measured by using the acceleration of gravity, errors would occur in the pitch and roll angle measurement if current position swiftly changes, and therefore, it is hardly applicable to the movable devices such as portable devices. Additionally, the requirement for slope detection device 120 increases the volume as well as the manufacturing cost of the device, and also, power consumption increases. The conventional approach is quite difficult to apply to the field of portable devices which is now receiving the most attention from many manufacturers.